Recently, in the field of machine tools, from an improved operation efficiency point of view, there is a need for a higher operational speed for a portion driven by fluid pressure such as hydraulic pressure, and from an improved mechanical efficiency point of view, there is a need for a reduction in a torque of a rotating portion which rotates while preventing leakage of a fluid.
Under such a circumstance, various types of sealing apparatus have been proposed have been proposed which have an improved sealing performance for a rotating portion which is subject to a high fluid pressure and rotates with a reduced torque.
As an example, as shown in FIG. 2A, there is a sealing apparatus in which, in order to seal an annular gap S formed between two inner and outer members 11 and 12 that coaxially rotate relative to each other, an O-ring (backup ring) 14 and a seal ring 15 fitted on its inner side are installed in an annular groove for sealing 13 which is formed on an inner surface portion of a shaft hole 11a of a first member (outer member) 11 along a peripheral direction, and inclined faces 15a, 15b are formed in a sliding surface of the seal ring 15 against a second member (inner member) 12 at both sides in an axial direction (a direction in which a fluid pressure P is applied). As shown in FIG. 2B, with such a sealing apparatus, when the fluid pressure P is applied, a fluid enters between the inclined surface 15a, which is on a side that comes into contact with an operating fluid (opposite pressure side), and the second member 12. Accordingly, an area of contact between the seal ring 15 and the second member 12 decreases and a frictional resistance between the seal ring 15 and the second member is reduced. Thus, an increased sealing performance and a reduced torque of the rotating portion can be achieved at simultaneously. (For example, see Patent Document 1).